INTERACTION BETWEEN THE EFFECTS OF PHYTOCHROME AND GIBBERELLIC-ACID ON THE SENESCENCE OF ALSTROEMERIA-PELEGRINA LEAVES

Chlorophyll loss in the leaves of cut flowering branches of Alstroemeria pelegrina L. cv. Stajello, placed in water in darkness at 20-degrees-C, was inhibited by irradiation with red light and by the inclusion of gibberellic acid (GA3) in the water. The effects of red light were abolished when it was followed by far-red light. Effects of GA3 and red light were additive over a range of GA3 concentrations (0.01-1 muM). Chlorophyll breakdown was increased by the inclusion of AMO-1618, ancymidol, or tetcyclasis in the water. The effect of these inhibitors of gibberellin synthesis was fully reversed by GA3. The inhibition of chlorophyll breakdown by red light was absent when AMO-1618, ancymidol or tetcyclasis were included in the water. The results indicate that leaf yellowing is controlled by endogenous gibberellins and that the effect of phytochrome is mediated by gibberellin synthesis.